Methods and system for launching a hybrid vehicle

Abstract

Systems and methods for launching a hybrid vehicle that includes a motor/generator and an automatic transmission with a torque converter are described. The systems and methods may permit improved vehicle acceleration to enhance hybrid vehicle performance during specific vehicle launch conditions. The launch conditions may be established based on brake pedal position and accelerator pedal position.

The invention claimed is: 
     
       1. A vehicle operating method, comprising:
 adjusting speed of a torque converter impeller from a first speed to a second predetermined speed in response to contemporaneously applying a brake pedal and an accelerator pedal, where the second predetermined speed is a speed where an engine and an electric machine have capacity to provide a combined first torque, the combined first torque greater than combined maximum torque output capacity of the engine and the electric machine operating at any speed other than the second predetermined speed. 
 
     
     
       2. The method of  claim 1 , where the second predetermined speed is a function of braking torque of driven wheels, and further comprising:
 starting an engine in response to contemporaneously applying the brake pedal and the accelerator pedal. 
 
     
     
       3. The method of  claim 2 , further comprising adjusting torque of the engine and torque of the electric machine after starting the engine to rotate the torque converter impeller at the second predetermined speed. 
     
     
       4. The method of  claim 3 , where the torque of the engine and the torque of the electric machine are adjusted responsive to a battery state of charge. 
     
     
       5. A vehicle operating method, comprising:
 adjusting speed of a torque converter impeller from a first speed to a second predetermined speed in response to contemporaneously applying a brake pedal and an accelerator pedal, where the first speed is a speed of a pump equal to or above which the pump provides hydraulic line pressure greater than a threshold pressure. 
 
     
     
       6. The method of  claim 5 , where the threshold pressure is a pressure sufficient to fully close transmission clutches. 
     
     
       7. A vehicle operating method, comprising:
 adjusting speed of a torque converter impeller from a first speed to a second predetermined speed in response to contemporaneously applying a brake pedal and an accelerator pedal; and 
 adjusting output torque of an engine to provide a threshold torque in response to releasing the applied brake pedal, where adjusting speed of the torque converter impeller from the first speed to the second predetermined speed includes adjusting speed of the torque converter impeller only after accelerator pedal position exceeds a threshold while a vehicle that includes the engine is stopped. 
 
     
     
       8. The method of  claim 7 , where the threshold torque is greater than maximum engine torque at any engine speed other than an engine speed where the threshold torque is provided. 
     
     
       9. The method of  claim 7 , where the second predetermined speed is a threshold speed based on a stall speed of a torque converter, the stall speed based on driven wheel braking torque. 
     
     
       10. The method of  claim 7 , where adjusting speed of the torque converter impeller from the first speed to the second predetermined speed includes adjusting speed of the torque converter impeller only after a threshold driven wheel braking torque is provided by applying the brake pedal. 
     
     
       11. The method of  claim 7 , further comprising reducing torque delivered to a powertrain via brake pedal torque. 
     
     
       12. The method of  claim 7 , further comprising limiting wheel slip to less than a threshold via modulating torque of an electric machine after releasing the brake pedal. 
     
     
       13. The method of  claim 7 , further comprising adjusting torque of an electric machine to provide a desired torque converter impeller torque while contemporaneously applying the brake pedal and the accelerator pedal, the desired torque converter impeller torque is a torque that rotates the torque converter impeller at the second predetermined speed. 
     
     
       14. A system, comprising:
 an engine; 
 a motor/generator; 
 a transmission mechanically coupled to the engine and the motor/generator, the transmission including a torque converter impeller; and 
 a controller including executable instructions stored in non-transitory memory to: 
 adjust speed of the torque converter impeller from a first speed to a second predetermined speed in response to contemporaneously applying a brake pedal to provide greater than a threshold amount of driven wheel braking torque and applying an accelerator pedal to a position that is greater than a threshold; and 
 cancel torque requested via the accelerator pedal in response to torque requested via the brake pedal when the accelerator pedal is at a position that is less than the threshold. 
 
     
     
       15. The system of  claim 14 , further comprising additional instructions stored in non-transitory memory to operate the engine at wide open throttle in response to releasing the applied brake pedal. 
     
     
       16. The system of  claim 15 , further comprising additional instructions stored in non-transitory memory to modulate torque of an electric machine to control wheel slip in response to releasing the applied brake pedal. 
     
     
       17. The system of  claim 14 , further comprising additional instructions stored in non-transitory memory to adjust torque of the motor/generator to provide a desired torque converter impeller torque that rotates the torque converter impeller at the second predetermined speed.